Diversity of aerobic endospore-forming bacteria in a tropical environment

Abstract

Genus and species diversity of aerobic endospore-forming bacteria in soil and water habitats was demonstrated. These genera include Bacillus, Thermoactinomyces, Sporolactobacillus and Sporosarcina. Of the 821 isolates characterized, 729 isolates were identified as 29 species of genus Bacillus. For each of the other non-Bacillus genera, a single species was isolated. Some isolates could not be identified to species level because their characteristics failed to much those of val idly described aerobic endospore formers. Samples were collected from different local habitats occurring within a geographical region: 35°8' E to 38°3'E and 0°0' to 2020'S. These sites represented Eco-clirnatic zones I-V. Isolation of these bacteria was made from both Soil and water samples. Forest soil samples were collected from the Nairobi arboretum and Mount Kenya forest belt while the grassland samples were collected from Karniti area and Mt. Kenya moorland. Dry arid soils of Kibwezi and the moraine soils of Mt. Kenya were also sampled. Garden soil sampleswere collected from Kitale-Cherangani area. Water samples were collected from five lakes of Mt. Kenya leeward side; Teleki, Hut, Galley, curling pond and Nanyuki tarns. Lake Naivasha, Malewa River, Chania River, Naro Moru River, acidic and alkaline springs of Mackinder's camp and bog areas of Mt. Kenya, were also sampled. The milky saps of two mountain plant species: Lobelia telekii and Senecio brassica were also analyzed for the presence of these bacteria. Most Bacillus isolates were gram positive but KOH negative rods, with ellipsoidal or spherical spores that were borne at a central, lateral, or a terminal position in swollen or unbulged sporangia. Most of these isolates e.g. Bicereus and Buhuringiensis had ellipsoidal spores in unbulged sporangia. However, only a few species e.g. Bipasteuri and B.sphaericlls had spherical spores. Most Bacillus isolates were catalase positive and produced acid but not gas from D-glucose or D-mannitol. Ability to hydrolyze various compounds including starch, and gelatine differed amongst various species while reduction of nitrates to nitrites was observed in most Bacillus species e.g. B.macerans. However, B. azotoformans reduced the nitrites to their gaseous components. Others had no observable action on these compounds. Parasporal crystals were only observed in